1. Field of Invention
The invention relates to a method for etching a metal-containing layer on a substrate using a plasma etching process and, in particular, a method for etching a differential metal gate structure.
2. Description of Related Art
As the size of semiconductor devices is reduced, process development and integration issues are key challenges for new gate stack materials including high-permittivity (or high dielectric constant) dielectric materials (also referred to herein as high-k materials).
Dielectric materials featuring a dielectric constant greater than that of SiO2 (k˜3.9) are commonly referred to as high-k materials. In addition, high-k materials may refer to dielectric materials that are deposited onto substrates (e.g., HfO2, ZrO2) rather than grown on the surface of the substrate (e.g., SiO2, SiNxOy). High-k materials may incorporate metallic silicates or oxides (e.g., Ta2O5 (k˜26), TiO2 (k˜80), ZrO2 (k˜25), Al2O3 (k˜9), HfSiO, HfO2 (k˜25)).
For front-end-of-line (FEOL) operations, in the near future, these high-k materials are contemplated for integration with polycrystalline silicon (polysilicon) gate structures and, in the longer term, they are contemplated for use with metal gates. However, the integration of high-k materials with polysilicon gate structures generally requires the insertion of a thin layer, such as a metal nitride, between the high-k layer and the polysilicon layer, where the thin layer may act as a barrier layer. This material must be etched while minimizing damage to the gate structure, etc. Furthermore, metal nitrides are contemplated for use in metal gates, and must be etched while minimizing damage to the underlying structure.
Of course, many other needs exist in semiconductor processing for etching a metal containing layer. One example includes etching portions of a metal containing barrier layer in a contact or via during metallization processes for back-end-of-line (BEOL) operations. Another example includes etching portions of metal containing layers in capacitors for DRAM production.